Method for controlling a DC motor and relative open-loop voltage mode controller

1. A method for controlling in an open-loop voltage mode a DC motor driven through a power amplifier, the method comprising: generating a control voltage for the DC motor to be input to the power amplifier based upon a difference between an external command and a correction signal; amplifying the control voltage for generating a replica of an output of the power amplifier; estimating current flowing in the DC motor based upon the replica of the output of the power amplifier and a model of the DC motor; and generating the correction signal proportional to the estimated current.

2. A method according to claim 1 , wherein generating the correction signal comprises: monitoring a speed of the DC motor; estimating a back electromotive force induced in a winding of the DC motor based upon the monitored speed; calculating a sum of the replica of the output of the power amplifier and the estimated back electromotive force; and wherein the estimated current is based upon the sum of the replica of the output of the power amplifier and the estimated back electromotive force.

3. A method according to claim 2 , wherein estimating the back electromotive force comprises multiplying the monitored speed by a certain value initially equal to a nominal torque constant of the DC motor; and further comprising: estimating an effective resistance of the DC motor; and updating the certain value by increasing its value proportionally to resistance increments with respect to a nominal resistance of the DC motor.

4. A method according to claim 1 , wherein the DC model is defined by a state space model in a discrete time domain.

5. A method for controlling a DC motor in an open-loop voltage mode, the method comprising: generating a control voltage to be input to a power amplifier connected to an input of the DC motor, the control voltage being based upon a difference between an external command and a correction signal; amplifying the control voltage for generating a replica of an output of the power amplifier; estimating current flowing in the DC motor based upon the replica of the output of the power amplifier and a model of the DC motor; and generating the correction signal proportional to the estimated current, the generating comprising monitoring a speed of the DC motor, estimating a back electromotive force induced in a winding of the DC motor based upon the monitored speed, and calculating a sum of the replica of the output of the power amplifier and the estimated back electromotive force.

6. A method according to claim 5 , wherein estimating the current flowing in the DC motor is based upon the sum of the replica of the output of the power amplifier and the estimated back electromotive force.

7. A method according to claim 5 , wherein estimating the back electromotive force comprises multiplying the monitored speed by a certain value initially equal to a nominal torque constant of the DC motor; and further comprising: estimating an effective resistance of the DC motor; and updating the certain value by increasing its value proportionally to resistance increments with respect to a nominal resistance of the DC motor.

8. A method according to claim 5 , wherein the DC model is defined by a state space model in a discrete time domain.

9. An open-loop voltage mode controller for a DC motor driven through a power amplifier, the controller comprising: a filter for generating a control voltage to be input to the power amplifier based upon a difference between an external command and a correction signal; a second amplifier for generating a replica of an output of the power amplifier; and an estimation circuit for estimating current flowing in the DC motor based upon the replica of the output of the power amplifier and a model of the DC motor, and for generating the correction signal proportional to the estimated current.

10. A controller according to claim 9 , wherein the DC motor comprises at least one winding, and a rotor associated with the at least one winding; and further comprising a correction circuit for generating a signal representing an estimated back electromotive force induced in the at least one winding of the DC motor based upon a speed of its rotor; and wherein the correction signal generated by said estimation circuit is also based upon the signal representing the estimated back electromotive force.

11. A controller according to claim 10 , further comprising: a feedback loop generating a feedback voltage representing an estimated value of the current circulating in the at least one winding of the DC motor based upon the control voltage and the estimated back electromotive force; and a proportional-integral controller receiving as input a difference between the external command and the feedback voltage, and outputting the control voltage to said filter.

12. A controller according to claim 11 , wherein the DC motor has a resistance and an inductance associated therewith; said feedback loop comprising: an adder receiving as input the replica of an output of the power amplifier signal output by said second power amplifier and the signal representing the estimated back electromotive force; and an R-L circuit having an estimated resistance and inductance based upon the resistance and inductance of the DC motor, said R-L circuit for generating the feedback voltage.

13. A DC motor assembly comprising: a DC motor; a power amplifier connected to an input of said DC motor; and an open-loop voltage mode controller connected to said power amplifier, said controller comprising a filter for generating a control voltage to be input to the power amplifier based upon a difference between an external command and a correction signal, a second amplifier for generating a replica of an output of the power amplifier, and an estimation circuit for estimating current flowing in the DC motor based upon the replica of the output of the power amplifier and a model of the DC motor, and for generating the correction signal proportional to the estimated current.

14. A DC motor assembly according to claim 13 , wherein said DC motor comprises at least one winding, and a rotor associated with said at least one winding; and wherein said controller further comprises a correction circuit for generating a signal representing an estimated back electromotive force induced in said at least one winding of the DC motor based upon a speed of said rotor; and wherein the correction signal generated by said estimation circuit is also based upon the signal representing the estimated back electromotive force.

15. A DC motor assembly according to claim 14 , wherein said controller further comprises: a feedback loop generating a feedback voltage representing an estimated value of the current circulating in said at least one winding of the DC motor based upon the control voltage and the estimated back electromotive force; and a proportional-integral controller receiving as input a difference between the external command and the feedback voltage, and outputting the control voltage to said filter.

16. A DC motor assembly according to claim 15 , wherein said DC motor has a resistance and an inductance associated therewith; said feedback loop comprising: an adder receiving as input the replica of an output of the power amplifier signal output by said second power amplifier and the signal representing the estimated back electromotive force; and an R-L circuit having an estimated resistance and inductance based upon the resistance and inductance of the DC motor, said R-L circuit for generating the feedback voltage.